Near Hall’s Hill, Virginia

March 8, 1862

The fever cases seems to multiply with each hospital visit I make. The physicians call it camp fever at first, but then—they fall silent. They exchange glances. “It transforms into something altogether different,” one surgeon told me yesterday, his voice low. “It is as though the devil himself takes residence within them.”

The afflicted become violent beyond all reason. They attack their own comrades—men who shared their tent...